The primary objective of this grant proposal is to use a novel Fas Ligand molecule (SA-FasL) with potent apoptotic activity and a unique method, designated as ProtExTM, to rapidly and effectively display SA-FasL at the protein level on antigen-presenting cells (APCs) or pancreatic islets as an immunomodulatory approach to prevent and/or treat insulin-dependent Type I diabetes mellitus (T1D). T1D is a chronic autoimmune disorder that affects a large number of people worldwide. Transplantation of whole pancreas or purified islets promises an efficient approach to achieving euglycemia in T1D patients. However, immune rejection limits long-term graft survival. Islet cell destruction is primarily mediated by T cells directed at unique pancreatic beta cell antigens. In this application, we propose to use SA-FasL to induce apoptosis in pathogenic autoreactive and alloreactive T cells for the prevention and treatment of diabetes. FasL-induced apoptosis is the main mechanism of activation-induced cell death responsible for immune homeostasis and is also important for tolerance to self-antigens. There is evidence in the literature suggesting that FasL is not only important for the induction of tolerance by inducing apoptosis in antigen-activated lymphocytes, but also for the maintenance of tolerance by facilitating the generation and function of immunoregulatory lymphocytes. Therefore, we hypothesize that immunomodulation with SA-FasL will effectively eliminate pathogenic autoreactive and alloreactive lvmphocytes and induce immunoregulatory mechanisms that will maintain tolerance. We have recently generated a modified form of FasL molecule, SA-FasL, with potent apoptotic activity and developed a novel approach to display SA-FasL at the protein level on the surface of any cell of interest within a short period of time (-2 hrs). In preliminary studies, we demonstrated that SA-FasL can also be effectively displayed on the surface of pancreatic islets without toxicity and these islets restored euglycemia upon transplantation into syngeneic diabetic mice. In this application, we propose to use SA-FasL with the ProtExTM technology to prevent diabetes in prediabetic NOD and treat diabetes in diabetic animals using allogeneic islet transplantation. Diabetes in NOD will be prevented by the treatment of prediabetic mice with SA-FasL as soluble protein or displayed on APCs pulsed with islet antigens. Diabetes in NOD will be treated by the transplantation ofC57BL/6 allogeneic islets displaying SA-FasL with and without FasL-APCs. The recognition of auto/alloantigens in the context of SA-FasL is expected to result in physical/functional elimination of pathogenic auto/alloreactive T cells and generation of protective immune mechanisms that maintain tolerance. Induction of tolerance will be followed by a series of studies to delineate the implicated mechanisms. Rapid and durable display of functional proteins on cells or tissues offers a whole new means of intervention in the areas of autoimmunity, transplantation, and vaccines. This approach possesses the simplicity, safety, and efficacy required to make it a clinically relevant alternative to gene therapy in the treatment of a broad spectrum of immune-based diseases.